Fix a bug introduced in "Fix multiplication producing a negative zero" that
caused the sign to be forced to +1 when A > 0, B < 0 and B's low-order limb
is 0.
Add a non-regression test. More generally, systematically test combinations
of leading zeros, trailing zeros and signs.
Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
No need to bypass the API to fill limbs. It's a better test to just
set the top bit that we want to have set, and it's one less bypass of
the API.
Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
mbedtls_mpi_read_binary{,_le} (in https://github.com/ARMmbed/mbedtls/pull/4276)
and mbedtls_mpi_read_string (in https://github.com/ARMmbed/mbedtls/pull/4644)
changed their behavior on an empty input from constructing an MPI object with
one limb to not allocating a limb. In principle, this change should be
transparent to applications, however it caused a bug in the library and it does
affect the value when writing back out, so list the change in the changelog.
Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
In mbedtls_mpi_read_string, if the string is empty, return an empty bignum
rather than a bignum with one limb with the value 0.
Both representations are correct, so this is not, in principle, a
user-visible change. The change does leak however through
mbedtls_mpi_write_string in base 16 (but not in other bases), as it writes a
bignum with 0 limbs as "" but a bignum with the value 0 and at least one
limb as "00".
This change makes it possible to construct an empty bignum through
mbedtls_mpi_read_string, which is especially useful to construct test
cases (a common use of mbedtls_mpi_read_string, as most formats use in
production encode numbers in binary, to be read with mbedtls_mpi_read_binary
or mbedtls_mpi_read_binary_le).
Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
Fix mbedtls_mpi_mul_mpi() when one of the operands is zero and the
other is negative. The sign of the result must be 1, since some
library functions do not treat {-1, 0, NULL} or {-1, n, {0}} as
representing the value 0.
Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
Shifting TA and TB before the loop is not necessary. If A != 0, it will be
done at the start of the loop iteration. If A == 0, then lz==0 and G is
correctly set to B after 0 loop iterations.
Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
In Mbed TLS 2.26.0, the bug was hard to trigger, since all methods for
parsing a bignum (mbedtls_mpi_read_xxx functions) constructed an mbedtls_mpi
object with at least one limb.
In the development branch, after the commit
"New internal function mbedtls_mpi_resize_clear", this bug could be
triggered by a TLS server, by passing invalid custom Diffie-Hellman
parameters with G=0 transmitted as a 0-length byte string.
Since the behavior change in mbedtls_mpi_read_binary and
mbedtls_mpi_read_binary_le (constructing 0 limbs instead of 1 when passed
empty input) turned out to have consequences despite being in principle an
internal detail, mention it in the changelog.
Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
Fix a null pointer dereference in mbedtls_mpi_exp_mod(X, A, N, E, _RR) when
A is the value 0 represented with 0 limbs.
Make the code a little more robust against similar bugs.
Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
Test both 0 represented with 0 limbs ("0 (null)") and 0 represented
with 1 limb ("0 (1 limb)"), because occasionally there are bugs with
0-limb bignums and occasionally there are bugs with removing leading
zero limbs.
Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
mbedtls_mpi_exp_mod can be called in three ways regarding the speed-up
parameter _RR: null (unused), zero (will be updated), nonzero (will be
used). Systematically test all three.
Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
Remove the RR parameter to the mbedtls_mpi_exp_mod test function.
It was never used in the test data, so there is no loss of functionality.
Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
Test mbedtls_mpi_safe_cond_assign() and mbedtls_mpi_safe_cond_swap()
with their "unsafe" counterparts mbedtls_mpi_copy() and
mbedtls_mpi_swap(). This way we don't need to repeat the coverage of
test cases.
Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
Similarly to "Overhaul testing of mbedtls_mpi_copy", simplify the code
to test mbedtls_mpi_swap to have just one function for distinct MPIs
and one function for swapping an MPI with itself, covering all cases
of size (0, 1, >1) and sign (>0, <0).
The test cases are exactly the same as for mbedtls_mpi_copy with the
following replacements:
* `Copy` -> `Swap`
* ` to ` -> ` with `
* `_copy` -> `_swap`
Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
Replace the two test functions mbedtls_mpi_copy_sint (supporting signed
inputs but always with exactly one limb) and mbedtls_mpi_copy_binary
(supporting arbitrary-sized inputs but not negative inputs) by a single
function that supports both arbitrary-sized inputs and arbitrary-signed
inputs. This will allows testing combinations like negative source and
zero-sized destination.
Also generalize mpi_copy_self to support arbitrary inputs.
Generate a new list of test cases systematically enumerating all
possibilities among various categories: zero with 0 or 1 limb, negative or
positive with 1 limb, negative or positive with >1 limb. I used the
following Perl script:
```
sub rhs { $_ = $_[0]; s/bead/beef/; s/ca5cadedb01dfaceacc01ade/face1e55ca11ab1ecab005e5/; $_ }
%v = (
"zero (null)" => "",
"zero (1 limb)" => "0",
"small positive" => "bead",
"large positive" => "ca5cadedb01dfaceacc01ade",
"small negative" => "-bead",
"large negative" => "-ca5cadedb01dfaceacc01ade",
);
foreach $s (sort keys %v) {
foreach $d (sort keys %v) {
printf "Copy %s to %s\nmbedtls_mpi_copy:\"%s\":\"%s\"\n\n",
$s, $d, $v{$s}, rhs($v{$d});
}
}
foreach $s (sort keys %v) {
printf "Copy self: %s\nmpi_copy_self:\"%s\"\n\n", $s, $v{$s};
}
```
Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
This is mostly to look for cases where the sign bit may have been left at 0
after zerozing memory, or a value of 0 with the sign bit set to -11. Both of
these mostly work fine, so they can go otherwise undetected by unit tests,
but they can break when certain combinations of functions are used.
Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
Replace calls to mbedtls_mpi_read_string() with a wrapper
mbedtls_test_read_mpi() when reading test data except for the purpose
of testing mbedtls_mpi_read_string() itself. The wrapper lets the test
data control precisely how many limbs the constructed MPI has.
Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
This test helper reads an MPI from a string and guarantees control over the
number of limbs of the MPI, allowing test cases to construct values with or
without leading zeros, including 0 with 0 limbs.
Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
- “Fix an issue where X happens” → ”Fix X“
the extra words are just a distraction.
- “resource” → “a resource”
- “where resource is never freed” has a name: it's a resource leak
- “when running one particular test suite” → “in a test suite”
Signed-off-by: Joe Subbiani <joe.subbiani@arm.com>
Remove a case that cannot be triggered as PSA_ALG_SIGN_GET_HASH always
returns 0 for raw algorithms.
Signed-off-by: Janos Follath <janos.follath@arm.com>
Hash and sign algorithms require the alignment of the input length with
the hash length at verification as well not just when signing.
Signed-off-by: Janos Follath <janos.follath@arm.com>
The psa_verify_hash() is the pre-hashed version of the API and supposed
to work on hashes generated by the user. There were tests passing that
were getting "hashes" of sizes different from the expected.
Transform these into properly failing tests.
Signed-off-by: Janos Follath <janos.follath@arm.com>
PSA Crypto always passed MBEDTLS_MD_NONE to Mbed TLS, which worked well
as Mbed TLS does not use this parameter for anything beyond determining
the input lengths.
Some alternative implementations however check the consistency of the
algorithm used for pre-hash and for other uses in verification (verify
operation and mask generation) and fail if they don't match. This makes
all such verifications fail.
Furthermore, the PSA Crypto API mandates that the pre-hash and internal
uses are aligned as well.
Fixes#3990.
Signed-off-by: Janos Follath <janos.follath@arm.com>
Hashes used in RSA-PSS encoding (EMSA-PSS-ENCODE, see §9.1.1 in RFC
8017):
- H1: Hashing the message (step 2)
- H2: Hashing in the salt (step 6)
- H3: Mask generation function (step 9)
According to the standard:
- H1 and H2 MUST be done by the same hash function
- H3 is RECOMMENDED to be the same as the hash used for H1 and H2.
According to the implementation:
- H1 happens outside of the function call. It might or might not happen
and the implementation might or might not be aware of the hash used.
- H2 happens inside the function call, consistency with H1 is not
enforced and might not even be possible to detect.
- H3 is done with the same hash as H2 (with the exception of
mbedtls_rsassa_pss_verify_ext(), which takes a dedicated parameter for
the hash used in the MGF).
Issues with the documentation:
- The comments weren't always clear about the three hashes involved and
often only mentioned two of them (which two varied from function to
function).
- The documentation was giving the impression that the standard
recommends aligning H2 and H1 (which is not a recommendation but a
must).
Signed-off-by: Janos Follath <janos.follath@arm.com>
